The problem might be an "open relay"! An open relay is a mail server that is incorrectly configured, such that it will allow anyone on the Internet to send mail to anyone else on the Internet. This allows junk e-mailers to use the mail server to send their mail, while remaining anonymous. It is estimated that up to 90% of all unwanted e-mail on the Internet is sent through open relays. Accepting mail from open relays would open up our mail server, and our users, to thousands of unwanted messages a day. Many ISPs and businesses use one method or another to filter or block mail from open relays, the most common of which is a subscription to a service that tracks currently open relays.
Our Internet provider subscribes to the Open Relay Database, ordb.org, which keeps a list of known open relays. In order for the mail to reach our mail server, the administrative authorities for your mail server need to be made aware of this problem, so that the mail servers can be reconfigured properly. Once the problem is corrected, they can have their mail servers removed from the ORDB list by going to:
Once removed from the ORDB list, our mail server will immediately begin accepting mail from those servers again. If you have any questions, or need more assistance in this matter, please check out www.ordb.org/faq.]